RESUMEN
The surface modification of mesoporous silica monoliths through thiol-ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol-gel hydrolysis-polycondensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3-mercaptopropyl)trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore-wall chemistries. Nitrogen sorption, small-angle X-ray scattering, solid-state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization. This report demonstrates that thiol-ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces.
RESUMEN
The behavior of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium dicyanamide [Emim][DCA] and 1-ethyl-3-methylimidazolium triflate [Emim][TfO], in (meso)porous carbonaceous hosts was investigated. Prior to IL incorporation into the host, the carbon matrix was thermally annealed between 180 and 900 °C to control carbon condensation and surface chemistry. The resulting materials have an increasing "graphitic" carbon character with increasing treatment temperature, reflected in a modified behavior of the ILs when impregnated into the carbon host. The two ILs show significant changes in the thermal behavior as measured from differential scanning calorimetry; these changes can be assigned to anion-π interaction between the IL anions and the pore wall surfaces of these flexible carbonaceous support materials.
RESUMEN
We have synthesized mesoporous silica monoliths functionalized with 2-(4-pyridylethyl)triethoxysilane 1 and N,N-dimethyl-pyridine-4-yl-(3-triethoxysilyl-propyl)-ammonium iodide 2. The organically modified silica monoliths were characterized via IR spectroscopy, nitrogen sorption, small angle X-ray scattering (SAXS), thermogravimetric analysis-differential thermal analysis (TGA-DTA), and acid-base titration. The degree of functionalization can be changed by the ratio of the functional silane to the silica precursor tetramethyl orthosilicate (TMOS). The functionalized silica monoliths were filled with 1-ethyl-3-methyl imidazolium [Emim]-X (X = dicyanamide [N(CN)2] or triflate [TfO]) ionic liquids (ILs) using an established methanol-IL exchange technique. The phase behavior of the resulting ionogels was investigated via differential scanning calorimetry (DSC). DSC curves show that the modification of the silica pore walls with organic groups strongly affects the phase behavior of the confined ILs. Modification with silane 1 completely suppresses the glassy state of [Emim][TfO] previously observed in unmodified silica monoliths (Göbel et al., Phys. Chem. Chem. Phys. 2009, 11, 3653). In contrast, modification with silane 2 leads to the appearance and disappearance, respectively, of a presumed additional phase in [Emim][TfO] and [Emim][N(CN)2] with varying degree of monolith functionalization. The data thus show that organic modification of silica matrix materials could be a viable approach for the tuning of ionogel properties.
RESUMEN
Mesoporous silica monoliths were prepared by the sol-gel technique and filled with 1-ethyl-3-methyl imidazolium [Emim]-X (X=dicyanamide [N(CN)2], ethyl sulfate [EtSO4], thiocyanate [SCN], and triflate [TfO]) ionic liquids (ILs) using a methanol-IL exchange technique. The structure and behavior of the ILs inside the silica monoliths were studied using X-ray scattering, nitrogen sorption, IR spectroscopy, solid-state NMR, and thermal analysis. DSC finds shifts in both the glass transition temperature and melting points (where applicable) of the ILs. Glass transition and melting occur well below room temperature. There is thus no conflict with the NMR and IR data, which show that the ILs are as mobile at room temperature as the bulk (not confined) ILs. The very narrow line widths of the NMR spectra suggest that the ILs in our materials have the highest mobility reported for confined ILs so far. As a result, our data suggest that it is possible to generate IL/silica hybrid materials (ionogels) with bulk-like properties of the IL. This could be interesting for applications in, e.g., the solar cell or membrane fields.
RESUMEN
Silica is an important mineral in biology and technology, and many protocols have been developed for the synthesis of complex silica architectures. The current report shows that silsesquioxane nanoparticles carrying polymer arms on their surface are efficient templates for the fabrication of silica particles with a star- or raspberry-like morphology. The shape of the resulting particles depends on the chemistry of the polymer arms. With poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) arms, spherical particles with a less electron dense core form. With poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI), star- or raspberry-like particles form. Electron microscopy, electron tomography, and small-angle X-ray scattering show that the resulting silica particles have a complex structure, where a silsequioxane nanoparticle carrying the polymer arms is in the center. Next is a region that is polymer-rich. The outermost region of the particle is a silica layer, where the outer parts of the polymer arms are embedded. Time-resolved zeta-potential and pH measurements, dynamic light scattering, and electron microscopy reveal that silica formation proceeds differently if PDMAEMA is exchanged for PMETAI.